Continuous spinning of cellulose solutions in strong mineral acids



I NOV. 16, F|NK ETAL CONTINUOUS SPINNING OF CELLULOSE SOLUTIONS IN STRONG MINERAL ACIDS Filed Aug. 28, 1939 3 Sheets-Sheet 1 Nov. 16, 19436 H. FINK ETA'. 2,334,615

CONTINUOUS SPINNING OF CELLULOSE SOLUTIONS IN STRONG MINERAL ACIDS FilKed Aug. 28. 1939 3 Sheets-Sheet 2 ln ven fors Hem/'ich fn/f @us/av Raf/7 Byheif Afforneys Rib/mrd /fofsfad/ w Aww Nov. 16, 1943. H. FINK ET AL 2,334,615

CONTINUOUS SPINNING OF CELLULOSE SOLUTIONS IN STRONG MINERAL ACIDS Filed Aug. 28, 1939 3 Sheets-Sheet 3 Patented Nov. l16, 1943 CONTINUOUS SPINNING F CELLIDSE S0- LUTIONS IN STRONG MINERAL ACIDS Heinrich Fink, Gustav Rath, and Richard Hofstadt, Wolfen, Kreis Bitterfeld, Germany; vested in the Alien Property Custodian Application August 28, 1939, Serial No. 292,254 In Germany August 30, 1938 4 Claims.

It is known to dissolve cellulose in mineral acids such as sulfuric acid and phosphoric acid and tov work up the solutions to form artificial shaped bodies such as fibers or lms.

The solutions of cellulose in strong mineral acids are distinguished from cellulose solutions in ammoniacal copper oxide and quaternary bases as well as from viscose by a much higher viscosity with the same content of cellulose, and by the rapid degradation to which the cellulose is subject in. strong mineral acid solutions.

These properties combinedly render the production and working up of useful spinning solutions very diiiicult. Owing to the high viscosity, the mixing of the mass to homogeneity is very slow, being slower, the larger the batch. Deaeration of the Ahighly viscous mass is impossible. If the solution is produced in a vacuum kneader it is impossible to transfer the solution to the spinning reservoir without introducing fresh air into the solution. On the other hand owing to .the rapid degradation of the cellulose a reduction of the time taken in dissolving the cellulose and in workingup the solution is desirable.

It is, indeed possible to reduce the rate of degradation of the dissolved cellulose by keeping the solution at a low temperature, but apart from the expense involved this possibility is limited in practice by the fact that the solution becomes more viscous the lower the temperature.

It has further been proposed to reduce the rate of degradation of the dissolved cellulose by reducing the vconcentration of the solvent acid below the concentration necessary for dissolution of the cellulose fibers by addition of a more dilute acid or of another diluent after the cellulose has been dissolved. Apart from thefact that the content of cellulose of the solution is thereby diminished to an undesirable extent, the gradation of the cellulose in this so-called "meta-stabilized solution is4 much more rapid than appears from the viscosity curve of the solution.

In working upV successive batches in the usual manner the diilculty arises that the solution exhibits from the outsetl an undesirable rate of degradation of the cellulose and that the degree of degradation varies greatly from the beginning to the spinning nozzle continuously alters its properties, thereby rendering the production of uniform products of high value impossible. Moreculties by making use of the known thel end of a batch, a sudden change in the degree of degradation occurringfat the beginning of each batch. Owing to the great viscosity of the solution one batch cannot be completely removed from the spinning reservoir before the next ybatch is introduced, so that residues of previous batches in an advanced state of degradation are mixed with the fresh batch. vThus the solution reaching over it is practically impossible to make the solutions to be worked up free from air.

The present invention overcomes these dimproperty of cellulose of swelling strongly in mineral acids/of a certain concentration, whereby the union between the ibers is so loosened that there is produced a suspension of fibers of a pasty consistency which can easily be made to ow like a liquid by means of pumps, worms, pistons and the like. We have found that in this suspension of fibers the degradation of the undissolved cellulose is so slow that it is of no practical significance.

Reference is made to the accompanying drawings in which:

Figure l shows diagrammatically a sectional view of an apparatus for carrying the invention into effect,

Figure 2 is a diagrammatic longitudinal section of an apparatus comprising pressure worms pension slowly forward at a uniform rate by pressure and thoroughly mixing with.' the acid by means of a stirring device, the cellulose dissolves rapidly. Preferably a dissolving chamber is arranged in the path to the spinning nozzle, and there may advantageously be a further chamber of a similar kind for homogenizing the solution, whereupon the solution can, if necessary, be

`passed through a filter which is connected directly with Athe nozzle for producing bers, foils, tubes or the like.

The only discontinuous process consists in the production of relatively small batches of the suspension, since in this phase there' is .no danger of ldegradation at the proper temperature, for instance 0 C. On the other hand once the suspension has entered the apparatus as much cellulose is dissolved per unit time as leaves'the apparatus in the same time. Since the dissolution is 4.bubbles is impossible owing rapid the quantity of solution present in the apparatus can be kept very small. For example the total capacity of an apparatus for dissolving 100 kg'. oi' cellulose Ain 24 hours `need not amount to more than 3 liters, even if chambers of capacity 2-3 liters for dissolving the cellulose and homolgfenizing thesolution are provided.v 'Ihis ensures 'that the time fromthe entry of a cellulose 'mole- Vtechnical'working of the .viscose or cupramm I. nium process. In consequence'.metahstabilization [of the solution. which of coursein cases in which it is required could be introduced into theproce'ss withoutdiillcultyg-can be entirely dispensed with.l

If the invention is carried out in such a manner that the suspension ofcellulose in a mineral acid is de-aerated instead of the cellulose solution ready for spinning, a completely air-free cellulose solution is obtained in whichformation oi' air space by the mass.

The deaeration of the suspension is naturally produced more rapidly and completely the poorer it is in cellulose, the degree of swelling of the cellulose being assumed to be in each case the same. For many purposes, however, it is solutions with the highest possiblel content ofcelluto the filling oi'. the

the piston 3 a circular motion which brings about a thorough admixture of the suspension with the dissolving acid, so that a clear cellulose solution leaves the chamber 8 through the pipe II. The solution after passing, if necessary, through a filter I1 is fed by metering pumps I2 to the spinning nozzles. 1

In this apparatus the solution isfed uniformly forward by the propulsion 4of the pistons 3. The

Isuspension is supplied by removing the lid 2 of the cylinder 'l whose piston 3 is for the time beingv .in its lowest position and nlling the cylinder e with suspension; When-the lid is screwed on the cylinder is'evacuated while the other 'piston 3 makesitsworking 'strokef When the latter reaches its highestposition vit vis stopped and at the same time the other piston 3 comes into oper-L ation, the cocks I being reversed. In this manner the suspension continually enters the chamber 8 and passes to the spinning nozzles through the pipe II while they cylinders I are charged discontinuously;

In the apparatus shown in Figure 2 the cellulose suspension is likewise fed alternately to at least two cylinders I and is deaerated through pipes provided with cocks 8 before proceeding further. In this` case the cylinders have no lids ingworm I3 by way of the valve 1a with the lose and the lowest possible content of swelling acid-that are required. Since the batches containing Athe minimum of swelling acid are 'too stiff to be well evacuated the process is so carried out that the suspension is formed with an excess oi' swelling acid and is deaerated, whereupon the suspension under a steady weak pressure. The cylinders I and pistons 3 can in this case be much weaker than those of Figure 1 since the actual feeding of the suspension is performed by the driven worm I3. The latter feeds the suspension into the dissolving chamber I4, which is excess is pressed of! in the apparatus itself. before Y entry of the mass into the dissolving chamber. Thismay-be done for example by forming the feeding device before the dissolving chamber as a pressure worm. The degree of pressure depends on the degree of swelling of the cellulose which is determined by'the concentration oi' theI swelling acid and, for instance, when using' sulfuria acid, increases especially rapidly in the region oi' 5 8560 per cent sulfuric acid.' I

- Referring-now to-'Figure 1, I denotes two similar pressure-tight cylinders of acid-resistingmateria] having removable lids 2. Machined pistons 3 having rods! of which .the lower parts are screw-threaded,VA are adapted tobe moved by the driving wheels 5, in the cylinders I The means for driving the wheels I are the motors'M and gears *5a. The cylinders are provided at their upper ends with pipes having cocks 6 and conf" nected with vacuumapparatus. -In order to prevent air` from being sucked in through lack of tightness of the stuiiing boxes and thepistonsa branch pipe I8 may be connected with the` lower lends of the cylinder. f

During upward movement of; either piston the contents ofthe cylinderV I is pressed through .a pipe provided with a cock 'I into the cylindrical dissolving chamber 8 in which an 'eccentrically arranged rollerV 8 rotates.` At the same time 'the calculated quantity of mineral acid of the con` centration required .ior dissolving the 'cellulose' is pumpedinto the chamberv 8 from a reservoir by means of a. pumpflil. Preferably the entries of the dissolving acid is distributed over the whole circumference of the chamber 8 v-by means 'ofa likewise provided With ya feeding worm and is supplied with dissolving -acid from the pipe I0. To enhance the mixing eifect a counter-worm as shown in Figure 3 (reference numerals 22-7-24) may also be provided in the dissolving chamber.

After leaving the dissolving chamber the solution passes to two or more homogenizing worms I5 which feed the solution through pipes II to the spinnerets.

Figure 3 s hows apparatus whichv is suited for the production of air-free solutions especially rich in cellulose..` Only one charging container I with x .stirrer- Ia and deaerating connection 6 is shown the other or others being assumed to lie outside the plane of the paper behind container vI a yreversal valve suchas 'Ia in Figure 2 being pro` vided between them. Into the container `I the suspension is fed with an excess oi' swelling acid while stirring'and is then deaerated'. The mass is ...The worm I3 in this caseacts as apressure worm g circular pipe with alarge number of -perforations The mass is theny fed through the homogenizlns in this case so thin that it runs under its own V'head into the.y chamber provided with .thel worm I3,'the.container's I being againused alternately.

as is indicated by its tapering form. The walls of the press-chamber are hollow, the wall I 6 being perforated to allow the excess of swelling acid to be extruded'into the tank 25 where it can be collected andl returned to the mixer in which the I cellulose is swollen. The suspensionv having a reduced content of swelling'acid is then fed into v,the dissolving chamber 22, to which acid is supplied from the pipe I0. v'The dlssolving'chamber 22 is provided with a-kneading pump of theusual worms I5 and pipes I`I tothe spinnerets.

those cases in which no particularly high output is required. The apparatus of Figures 2 and 3 von the other hand work more quickly owing to the distribution of pressure over the whole appa- .ratus, and are especially advantageous in those cases in which a large output is required.

In all cases it is advantageous to provide the whole apparatus from the charging containers to .the spinnerets with a cooling jacket through which brine at about C. is circulated. The jacket is not shown in the drawings for the sake of clarity.

The invention is illustrated by the following examples:

Example 1 With every 3 kg. of cellulose (air-dry) there are stirred, while cooling to 0 C., 30 kg. of sulf-uric acid containing 59.0 per cent of HzSO4 and the mixture is fed into the similarly cooled cylinder l shown in Figure 1 or Figure-2 and evacuated. From there the suspension is ied'continuously during about 30 minutes by means of the piston 3 into the dissolving chamber 8, which is Example 2 4.5 kg. of cellulose (air-dry) in 45 kg. of sulfuric acid containing 59.5 per cent of H2SO4 are introduced into the container shown in Figure 3 and stirred at 0 C. The mixture is then evacuuated. The containers are used alternately. After evacuation the batch is run into the chamber containing the pressure worm i3 which expresses 16 kg. of swelling acid per batch, so that the mass enters the dissolving chamber with a content of 29 kg. of swelling acid to 4.5 kg. of cellulose. 9.5 kg. of sulfuric acid containing '75 per cent of H2SO4 and cooled to 0 C. are supplied to the dissolving chamber. The solution produced contains 9.8 per cent of cellulose and 57 per cent of H2S04. e

We claim:

1. A process of continuously producing solutions of cellulose in a strong mineral acid which comprises suspending the cellulose in a mineral acid of a concentration which will cause swelling of the cellulose, but will not dissolve it, feeding said suspension continuously to an extruding device and adding to said suspension on its way to the extruding device a strong mineral acid in an amount which is necessary to dissolve the cellulose in said suspension, the amount of solution formed per time unit being kept the same as the amount of solution leaving the extruding device. v l5 2. A process as claimed in claim 1 where the mineral acid lin the suspension is sulfuric acid with a content of about 59 per cent 'of H2504 and the strong mineral'acid dissolving the suspension is sulfuric acid of about '15 per cent of H2SO4. 3. A process of continuously producing solutions of cellulose in a strong mineral acid which comprises suspending the cellulose in a mineral l acid of a concentration which will cause swelling of the cellulose but will not dissolve it, continuously removing a part of the vsuspension liquid from the suspension, feeding said suspension continuously to an extruding device and adding .to Y

said suspension on its way to the extruding device a strong mineral acid in an amount which is necessary to dissolve the cellulose in said suspension, the amount of solution formed per time unit being kept the same as the amount of solution leaving the extruding device.

4. A process of continuously producing solutions of cellulose in a strong mineral acid which comprises suspending the cellulose in a minera1 acid of a concentration which will cause swelling of the cellulose but will not dissolve it, de-aerat- 4o ing the suspension, feeding said suspension continuously to an extruding device and adding to said suspension on its way to the extruding device a strong mineral acid in an amount which is necessary to dissolve the cellulose in said sus- 45 pension, the amount of solution formed per time unit being kept the same as the'amount of solution leaving the extruding device.

HEINRICH FINK. GUSTAV RTH. RICHARD HOFSTADT. 

